Purine-based chemical probe with HOMO switching for intracellular detection of mercury ions

The detailed photophysical characterization of 2-piperidinyl-6-triazolylpurine derivatives and their complexes with metal ions is presented. The studied compounds contain two electron donating units - piperidine and methoxyphenyl, while triazolyl-purine acts as an electron acceptor. These derivatives possess good fluorescence quantum yields in both aprotic and aqueous environments. All piperidine-triazole-purine compounds exhibited a fluorescence "turn-off" sensing behavior to different metal ions, including Hg²⁺. We are discussing the changes in photophysical properties occurring upon complexation including switching between highest occupied molecular orbitals (HOMOs) of different electron donating units and the entire electron charge shift possibility in the complex with mercury ion. The sensing concept was further applied for newly synthesized water-soluble compounds, that demonstrated better selectivity toward Hg²⁺ in aqueous media. Further, the selected 2-piperidinyl-6-triazolylpurine water-soluble derivative was employed as a "turn-off" chemical probe for mercury ion detection in living cells.